1. Field of the Invention
The present invention relates to a method for measuring the performance and controlling the levels of polymeric dispersants and other treatment chemicals in industrial cooling and boiler water systems.
2. Description of the Related Art
Maintaining proper residual levels of water treatment chemical actives is critical to the success of high-performance water treatment programs. To function properly, these programs rely on numerous active components including polymers, phosphonates, azoles, chelants, oxygen-scavengers, and, frequently, inorganic inhibitors such as phosphate and zinc. To provide optimum cost and performance, each active component in the water treatment program must be consistently maintained at residual levels sufficient to achieve treatment efficacy without relying on unnecessarily high levels of treatment chemicals.
Traditionally, treatment residuals have been monitored and controlled by analyzing grab samples and manually adjusting chemical feed based on the results of the testing. Tests that are frequently run using this approach include phosphate, phosphonate, and molybdate. Relatively simple colorimetric tests are readily available for these ingredients and have been used for many years. In contrast, simple analytical tests have generally not been available for directly measuring residual polymer levels. Techniques that have emerged rely on the use of inert fluorescent tags attached to the polymer as described in "Tagged Polymer Technology for Improved System Monitoring and Control" Corrosion 93, NACE, Paper 397, 1993. More recently, specific proteins have been attached to the polymer which give a response to an antibody test as described for example in "Toward Field Traceable Polymeric Dispersants" 58.sup.th International Water Conference, Nov.1-5, 1997, Pittsburgh, Pa. However, because both the fluorescent tag and the antibody tests are measuring the level of the polymer indirectly, aggressive system environments sufficient to separate the polymer from the tag or degrade the tag will render the tests unreliable. Further, because the basic polymer must be modified in order to be detected by these tests, the majority of commercially available polymeric dispersants are rendered unsuitable.
In solution, a polymer may function as a dispersant with respect to existing particulates and it may also inhibit the formation or growth of scale forming particles. When a polymer is added to a water treatment system it typically reacts both chemically and physically. Some portion of the added polymer may be adsorbed onto immobile surfaces or may be thermally, chemically, or biochemically degraded as a result of system conditions. This polymer, whether rendered immobile or degraded, is essentially lost from the system and will not be detected by sampling the system water. This loss of polymer has been termed "Polymer Demand." The remaining polymer is essentially present in three forms; unreacted polymer, polymer associated with inhibited particles functioning as a scale inhibitor, and polymer absorbed onto undeposited scale functioning as a dispersant.
Recently introduced polymer test methods, however, are typically either indiscriminate or limited as to which forms or form of polymer may be measured by the disclosed test method. The antibody test, for instance, measures only the unreacted polymer. In light of this limitation, the proponents of the antibody test have suggested that simply maintaining a measurable level of unreacted polymer indicates that there is sufficient polymer available for the desired inhibition and dispersant functions.
In contrast to the antibody method, the fluorescent tagged polymer test measures the system polymer demand by comparing the levels of the tagged polymer and an inert fluorescent tracer fed at fixed ratio to the tagged polymer. The proponents of the fluorescent tagged polymer test recognize that the polymer demand increases as the severity of operating conditions increase, but do not suggest a method for distinguishing between various forms of polymer that will be found in the system. Consequently, although the disclosed method for using the fluorescent tagged polymer test to monitor the system polymer demand can determine if the minimum dosing requirements are being met, this method does not detect instances in which the polymer and/or other treatment chemicals are being overdosed.